The invention relates to a rotary hammer with a pneumatic impact mechanism which comprises a reciprocating piston driving a beat piece. The impact mechanism is capable of being driven by means of a drive element rotatably mounted on a driven drive shaft. The drive element can be displaced axially relative to the drive shaft and brought into engagement with a coupling element fast on the drive shaft.
In a known rotary hammer of this type (DE-OS No. 24 49 191) there is fixed or non-rotatably formed on the drive shaft a ring-shaped coupling element having an outer surface shaped as a tapering truncated cone. Also on the drive shaft there is rotatably mounted a drive element which carries in an obliquely set annular groove a rotatable ring with a radially projecting pin. This pin is in engagement with the rear end of a piston arranged in a guide tube in which there is also a beat piece between which and the piston a driving excess pressure is built up in operation, as is known for penumatic impact mechanisms of rotary hammers (EP-A 015 185). In order to drive the impact mechanism of the known rotary hammer, the drive shaft carrying the coupling element is axially displaced against spring pressure at the work-piece by contact pressure of the tool held in the tool-holder of the rotary hammer, so that the truncated-cone-shaped peripheral surface of the coupling element is pressed into coupling engagement with a correspondingly truncated-cone-shaped annular surface of the drive element, and thus the drive element is rotated together with the driven drive shaft.
This known rotary hammer has a relatively complicatedly constructed drive element which consists of several parts and consequently requires expensive assembly. In addition, on account of the use of an axially displaceable drive shaft, there is also a relatively larger construction expense.